Throw catchable error when firebase.js wasn't loaded

[filiph]

initializeApp() should throw something like JsNotLoadedError when the wrapped JS functions and objects aren't available.

For example, when using the web app offline, firebase.js won't be loaded, and initializeApp() will die horribly with a null pointer exception, thus taking the whole app down.

[Janamou]

Will do, thanks!

[kevmoo]

As of ef44d79 we're pretty close. Leaving this open, since there are a number of APIs that are still not throwing as you'd expect.

[Ehesp]

Hey @kevmoo any updates on this one? We're implementing web support on FlutterFire and currently we're having to do hard try-catch blocks on the error, e.g:

	  try {
        app = firebase.app();
      } catch (e) {
        if (e.toString().contains("Cannot read property 'app' of undefined")) {
          throw coreNotInitialized();
        }

        rethrow;
      }

I noticed there is an internal _firebaseNotLoaded function which doesn't seem to be capturing this issue. Thanks!

[russellwheatley]

Our CI has been failing because the error message for this changed: 81dc72f (#6977)